The Dbl oncogene product as a GDP/GTP exchange protein for the Rho family: its properties in comparison with those of Smg GDS.

The dbl oncogene product (Dbl) showed the GDP/GTP exchange protein (GEP) activity on all the rho family small GTP-binding protein (G protein) members including RhoA and Rac1 as well as mCdc42. Dbl was active on both the lipid-modified and -unmodified forms of these small G proteins, but was much more active on the former form than on the latter form. In the presence of Rho GDI, an inhibitory GEP for the rho family members, the GEP activity of Dbl was markedly reduced. These properties of Dbl were partly different from those of Smg GDS, another GEP which is active not only on the rho family members but also on Ki-Ras and Rap1 and is active only on their lipid-modified form.